1. Field of the Invention
The present invention relates generally to ink-jet printing technology methods and apparatus and, more specifically, to a method and apparatus for aligning ink-jet pens firing droplets of a clear fluid.
2. Description of the Related Art
The art of ink-jet technology is relatively well developed. Commercial products such as computer printers, graphics plotters, copiers, and facsimile machines employ ink-jet technology for producing hard copy. The basics of this technology are disclosed, for example, in various articles in the Hewlett-Packard Journal, Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6 (December 1992) and Vol. 45, No. 1 (February 1994) editions. Ink-jet devices are also described by W. J. Lloyd and H. T. Taub in Output Hardcopy [sic] Devices, chapter 13 (Ed. R. C. Durbeck and S. Sherr, Academic Press, San Diego, 1988).
In U.S. Pat. No. 5,635,969 (Allen, assigned to the common assignee of the present invention and incorporated herein by reference), METHOD AND APPARATUS FOR THE APPLICATION OF MULTIPART INK-JET INK CHEMISTRY, a multi-color ink-jet printing system includes a printing element for apply a precisely metered quantity of a colorless precursor to a recording medium surface. The precursor conditions the medium surface prior to application of one or more colorants to the recording medium surface to prevent cockle and curl and to reduce dry time, while conditioning the recording surface for uniform dot gain independent of media composition. U.S. patent application Ser. No. 09/069,717, entitled REACTIVE INK SET FOR INK-JET PRINTING, by Askeland et al., and U.S. patent application Ser. No. 09/069,616, entitled MULTI-CHAMBER FLUID SUPPLY, by Askeland et al., and Related Applications cited therein are also assigned to the common assignee of the present invention and are incorporated herein by reference. Hereinafter, clear fluids used to affect ink dry time and permanence and to prevent cockle and curl of the print medium are generically referred to as "fixers."
In U.S. Pat. No. 5,600,350 (Cobbs et al., assigned to the common assignee of the present invention and incorporated herein by reference), MULTIPLE INKJET PRINT CARTRIDGE ALIGNMENT BY SCANNING A REFERENCE PATTERN AND SAMPLING SAME WITH REFERENCE TO A POSITION ENCODER, a method and apparatus for multiple ink-jet print cartridge alignment is provided by scanning a reference pattern and sampling with an optical sensor. In effect, a given test pattern is printed and actual print image data is compared to determine any misregistration of the cartridges. A SYSTEM AND METHOD FOR ESTABLISHING POSITIONAL ACCURACY IN TWO DIMENSIONS BASED ON A SENSOR SCAN IN ONE DIMENSION, also to the common assignee herein and incorporated by reference, is provided in U.S. Pat. No. 5,796,414 (Sievert et al.).
While the method of printing a test pattern and optically detecting actual positions of element of the pattern on the print media provides a valuable tool for colorants that have a sufficient reflectivity difference with respect to the background media, a problem arises with colorants that have a reflectance only a few percent different than the reflectance of the blank media. In U.S. patent application Ser. No. 08/636,439, for SYSTEMS AND METHOD FOR DETERMINING PRESENCE OF INKS THAT ARE INVISIBLE TO SENSING DEVICES (Nelson et al., assigned to the common assignee of the present invention and incorporated herein by reference), a system and method for determining the presence of inks that are visible to the normal human eye, but optically "invisible" to sensors is provided.
There remains a need for a method and apparatus for aligning an ink-jet print cartridge which prints a clear fluid on the print medium